Most noncardia gastric cancers are attributable to chronic mucosal inflammation due to Helicobacter pylori infection and some tumors also contain monoclonal Epstein-Barr virus (EBV). We are studying the descriptive epidemiology of this disease and the roles of EBV infection and of inflammation gene polymorphisms in its etiology. We are studying clonal expansion of lymphocytes as a potential precursor of non-Hodgkin's lymphoma in HIV infection and the general population, using multiple prospective cohorts with banked peripheral blood cells. IIB studies have implicated cytokine signaling dysregulation as an important etiologic factor for AIDS-related lymphoma. Both elevated blood levels as well as genetic variation in these pathways are predictive of subsequent lymphoma risk. Despite marked advances in antiretroviral therapy, cancer continues to be a major source of morbidity in AIDS.